Benefits of a closed loop control system for treating diabetic conditions by monitoring glucose levels and adjusting delivery rate of insulin are well known. Such systems, referred to as artificial pancreas, model healthy pancreas which, when functioning normally, produces insulin (by the beta cells (β-cells)) to counteract the rise in glucose levels in the blood stream. As is known, Type-1 diabetes mellitus condition exists when the beta cells in the pancreas either die or are unable to produce a sufficient amount of insulin naturally in response to the elevated glucose levels.
Common treatment of Type-1 diabetes is the use of insulin pumps that are programmed to continuously deliver insulin to the body through an infusion set. The use of insulin pumps to treat Type-2 diabetes (where the beta cells in the pancreas do produce insulin, but an inadequate quantity) is also becoming more prevalent. Such insulin delivery devices are preprogrammed with delivery rates such as basal profiles which are tailored to each user, and configured to provide the needed insulin to the user. Additionally, the preprogrammed delivery rates may be supplemented with periodic administration of bolus dosages of insulin (for example, correction bolus or carbohydrate bolus) as may be needed by the user.
In addition, continuous glucose monitoring systems have been developed to allow real time monitoring of fluctuation in glucose levels. One example is the FreeStyle Navigator® Continuous Glucose Monitoring System available from Abbott Diabetes Care Inc., of Alameda, Calif. The use of such glucose monitoring systems provides the user with real time glucose level information. Using the continuous glucose monitoring system, for example, diabetics are able to determine when insulin is needed to lower glucose levels or when additional glucose is needed to raise the level of glucose.
With the continued rise in the number of diagnosed diabetic conditions, there is on-going research to develop closed loop control systems to automate the insulin delivery based on the real time monitoring of the fluctuation in the glucose levels. Closed loop control algorithms such as, for example, proportional, plus integral, plus derivative (PID) control algorithm or model predictive control algorithm exist and are used to control the automatic delivery of insulin based on the glucose levels monitored. One key concern in such automated systems is safety. For example, the glucose sensor in the closed loop control system may enter failure mode (permanently or temporarily) in which case the monitored glucose level in the closed loop control system will introduce error and potentially result in an undesirable or dangerous amount of insulin being administered. Additionally, the infusion component in the closed loop control system may have errors or experience failure modes that result in an inaccurate amount of insulin delivered to the user.
Indeed, safety considerations as well as accuracy considerations to address and/or minimize the potential unreliability in the components of the closed loop control system are important to provide a robust control system in the treatment of diabetic conditions.